Ever wonder what it would be like to get shot in the head, or have your face smash into a car's windshield? Well, you can stop wondering, because you'll never know — even if it does happen to you.

There are at least two major reasons why, if you die in a sudden and violent fashion, you'll literally never know what hit you. First, our brains process information too slowly. Second, there's the issue of the integrity of the cognitive functions that are responsible for conscious experience. Let's take those one by one.

Eagleman says that it takes time for signals to move through the brain's grey matter that's situated around the cortex. These signals travel at a rate of one meter per second — a speed that Eagleman says is "insanely slow," when compared to electricity. "It takes a while for the brain to know what's happening," he says, "so we're always living in the past." In fact, Eagleman points out that our autonomous motor systems actually react faster to external stimuli than conscious awareness.

To get an appreciation of the slowness of human perception, Eagleman says it's helpful to compare it to the speed of mechanical devices. Take the anatomy of a car accident for example. It takes as long as 150 to 300 milliseconds (ms) to be aware of a collision after it happens. Other neuroscientists think it can take as much as 500 ms.

Now this might not sound like a lot of time, but think of what happens during a car accident. At the 1 ms mark, the car's pressure sensor detects a collision, and at 8.5 ms the airbag system fires. At the 15 ms mark, the car starts to absorb the impact to a significant degree. It's not until the 17 ms mark that the occupant starts to make contact with the airbag, with the maximum force of the collision reaching its apex at the 30 ms point. At the 50 ms mark, the safety cell begins to rebound, and after 70 ms the passenger moves back towards the middle of car — the point at which crash-test engineers declare the event as "complete."

And then, around the 150 to 300 ms mark, the occupant finally becomes aware of the collision.

That's assuming of course that an airbag was deployed or that the occupant was wearing a seatbelt. Otherwise, the person wouldn't have known that they were even in a car accident.

Which, if the accident was fatal, is not necessarily a bad thing.

No brain, no mind

If the parts of your brain that give rise to consciousness are severely impaired, then all awareness comes to a grinding halt. These all-important areas include the frontal cortex (attention and short-term memory), thalamus (regulation of consciousness and alertness), temporal gyrus (perception and comprehension), and the hippocampus (memory and spatial awareness). According to Eagleman, damage to the cortex and thalamus will often induce a comatose state.

But not all brain trauma is catastrophic in this way. Eagleman notes that conscious awareness can remain intact when the cerebellum (the "mini brain") is damaged. Moreover, it's not yet known how consciousness gets built from pieces of these parts.

"The whole system does seem to be involved in conscious awareness," says Eagleman, "but as more parts of the brain gets damaged, consciousness gets degraded." Consciousness is a fragile thing that appears to be dependent on consistent electrical signals traveling around the brain. Subsequently, hard blows to the head will cause the system to "reboot". When experiencing a massive head trauma, like a head hitting a dashboard, the brain is smashed around the inside of the skull, often causing fatal results - results that could never really be perceived.

Bullets in the brain

Interestingly, bullets can cause different problems than blunt brain trauma. As Rachel Swaby noted in her article, "What Happens When You Get Shot in the Head," a victim may have no chance of responding to what's happening. A bullet travels through the brain faster than the speed at which tissues tear. They push tissues out of the way, stretching them beyond their breaking points — and that's when the problems start:

You may or may or may not see it coming, but it doesn't really matter. You're not going…
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The ability to process information and solve problems? All gone when the bullet shoves its way through your prefrontal cortex. Your ability to index memories? Gone with your hippocampus. In the bullet's wake, a long temporary cavity is left. When the tearing finally does happen, your tissues will snap back toward the initial opening and overshoot their original position. You know that back and forth thing that happens when you kick one of those springy door stops? Well that's what your tissues do when the shock waves kick them.

Now that said, it's well documented that some people can survive being shot in the head. In fact, one-third of patients with a gunshot wound to the head survive, though 50% of them don't survive longer than 30 days. And those that do survive tend to have to deal with severe cognitive impairments. In most of these cases, the bullet did not cross through the midline, which is almost always fatal.

Eagleman says that many people survive shots to the head because bullets are relatively small and travel at high velocity. When shot just right, a bullet can quickly enter and exit the skull without inflicting too much damage.

Perhaps the best example of someone surviving a gunshot wound is the remarkable story of former Arizona Congresswoman Gabrielle Giffords. In her case, the bullet entered at the back of her skull and exited through the front, travelling through the left side of her brain. For Giffords, the areas affected included her speech centers and other non-life threatening functions. Moreover, surgeons did not have to remove much dead brain tissue and they were able to subdue swelling. They also didn't have to deal with any dangerous infections.

Giffords is clearly very lucky to be alive.

But as for those brain injuries that can quickly turn the insides of your skull into mush, I wouldn't worry too much about it. You'll be going from zero to oblivion faster than you can finish reading this sentence.